1. Technical Field
The present invention relates to medical image analysis, and more particularly, to a system and method for linking volumes of interest (VOIs) across timepoints for analysis of disease progression or response to therapy.
2. Discussion of the Related Art
Functional imaging using single photon emission computed tomography (SPECT) and positron emission tomography (PET) is extremely valuable in the diagnosis of various medical disorders. Uncertainty in the anatomic definition on SPECT and PET images, however, sometimes limits their usefulness. To overcome this, a combination of magnetic resonance images (MRI) and X-ray computed tomography (CT) images with functional SPECT or PET images of the same sections of the body is sometimes used. This provides complementary anatomic (MRI or CT) and physiological (SPECT or PET) information that is of great importance to research, diagnosis and treatment.
Functional body images and structural images are two types of medical images used by medical practitioners for the diagnosis of certain medical disorders. Functional body images such as those derived from SPECT or PET scans, provide physiological information, whereas structural images such as those derived from CT or MRI, provide an anatomic map of the body. Different medical imaging techniques may provide scans with complementary and occasionally conflicting information. For example, the combination of such images (via image fusion or image registration) using picture archiving communications systems (PACS) can often lead to additional clinical information not apparent in the separate images. Thus, by imposing a structural anatomic framework on a set of functional images, the position of a tumor or other lesion in a later functional image may be determined even where there is insufficient anatomic detail.
Although the construction of a composite, overlapping medical image with image registration has been primarily used in the fusion of functional and anatomical images, it has also been applied to a series of the same modality of images. Examples of this are registration of SPECT images of the same subject in follow-up studies or in a comparison of an image with normal uptake properties to an image with suspected abnormalities. In addition, image registration of SPECT and PET images and the registration of SPECT and PET images with anatomic atlases provide an important means to evaluate comparative uptake properties of SPECT and PET radiopharmaceuticals, and to correlate uptake properties with anatomy.
Multi-modal medical image registration is fast becoming a visualization tool that can significantly aid in the early detection of tumors and other diseases and aid in improving the accuracy of diagnosis. For example, radiologists often have difficulty locating and accurately identifying cancer tissue, even with the aid of structural information such as CT and MRI because of the low contrast between the cancer and the surrounding tissues in CT and MRI images. However, by using SPECT and radioactively labeled monoclonal antibodies it is possible to obtain high contrast images of the concentration of antibodies in tumors.
It is thus becoming increasingly desirable to combine the output and strengths of multiple medical imaging systems. However, certain drawbacks exist due to combining different file structures, the transfer and networking thereof and registration and visualization of the composite images. For example, such systems typically do not support more than a few combinations of datasets from different modalities. In addition, many systems do not provide a quick and accurate means for analyzing changes in tumors. Further, many systems do not provide a quick technique for aligning medical images from different timepoints. For example, to accurately analyze changes in tumors, it is often necessary to compare images of the same modality that were scanned at different timepoints.
Accordingly, there is a need for a technique that enables medical practitioners to compare patient scans taken at a different times using the same or different modalities so that medical practitioners can make better-informed diagnostic, therapy and follow-up decisions in a cost-effective and efficient manner.